1. Field of the Invention
The present invention relates to a gas turbine combustor and, particularly, to a gas turbine combustor of the pre-mixing type.
2. Description of the Related Art
Gas turbines have been extensively used in a variety of fields such as electricity generating plants, etc. Gas turbines produce power by rotating turbine blades using the combustion gas which is generated in a combustion chamber, by injecting fuel into air that has reached a high temperature after being compressed by a compressor, or by injecting the fuel into a premixture of air and fuel. In order to improve the efficiency of the gas turbine, it is desired that the temperature of the combustion gas at the inlet of the turbine blades is as high as possible, and efforts have been made to increase the temperature of the combustion gas.
In recent years, however, it has been urged to decrease nitrogen oxides (NOx) to meet exhaust gas regulations. NOx increases rapidly when the combustion gas is heated to a certain temperature. To decrease NOx, a maximum temperature of the combustion gas must be suppressed to not exceed the temperature at which NOx starts to increase rapidly.
The temperature of the combustion gas depends on the amount of air for combustion relative to the amount of fuel at the time of combustion; i.e., the temperature of the combustion gas decreases with an increase of the amount of the air for combustion and increases with a decrease of the amount of the air for combustion. To decrease NOx, therefore, it is necessary to accomplish combustion with a lean air-fuel ratio by increasing the amount of the air for combustion.
It has therefore been attempted to stabilize the flame to obtain combustion with a lean air-fuel ratio. For example, Japanese Unexamined Patent Publication (Kokai) No. 6-129640 discloses a cone that expands like a megaphone near the outlet of a pilot nozzle (see FIGS. 7A and 7B). In the combustor of this structure, however, a pre-mixture blown out from the swirling passages flows nearly parallel to the center axis of the turbine whereas the pilot flame flows along the inner surface of the pilot cone, so that the two meet at some angle. Besides, since the flow velocities are different between them, a great disturbance occurs in this region, and the flame loses stability making it difficult to make the fuel density lean to a sufficient degree to decrease NOx.
In view of the above-mentioned problem, it is an object of the present invention to provide a gas turbine combustor capable of accomplishing combustion even at a lean fuel density, while maintaining good combustion stability to decrease NOx.
According to the present invention, there is provided a gas turbine combustor in which plural pre-mixers that inject fuel into swirling air passages are arranged to surround a pilot burner, and a pilot flame, guided by a pilot cone in the shape of a flaring pipe and provided at the rear end of the pilot burner, is mixed with a pre-mixture blown out from the pre-mixers to obtain a combustion gas, wherein the gas turbine combustor comprises flame-stabilizing means which lower the disturbance in a region where the pre-mixture and the pilot flame are mixed to stabilize the pilot flame, so that the flame generated by igniting the pre-mixture with the pilot flame is stabilized.
The present invention may be more fully understood from the description of the preferred embodiments of the invention set forth below, together with the accompanying drawings.